Incorporation of zwitterionic push-pull chromophores into hybrid organic-inorganic matrixes

Dihydroxy-functionalized zwitterionic push-pull chromophores have been synthesized and incorporated into 3-glycidoxypropyltrimethoxysilane- and N-[(3-trimethoxysilyl)propyl]-ethylenediamine-derived hybrid materials. The functionalization allowed the dye to form covalent bonds to the matrix network, reaching up to 5% molar concentration without aggregation. The host hybrid material was also specifically designed to reduce photobleaching of the dye and to avoid the protonation of the carbanionic species that occurs in acidic media. The host material exhibits very good film-forming properties, and thick highly transparent doped layers can be fabricated via dip-coating. Upon incorporation into the matrix, the dye exhibits a reduction of photobleaching due to the scavenger effect of the amine groups. The strong negative solvatochromism exhibited by this class of chromophores was used to probe the physical-chemical environment within the pores. Dye-functionalized hybrid sol-gel materials were submitted to poling experiments, and the second harmonic signal was measured. Good temporal stability of the NLO materials (retention of ca. 85% of the initial signal value) was recorded after 3 months, providing a d33 value equal to 0.66 pm/V. This system represents one of the few examples of the successful incorporation of zwitterionic push-pull chromophores in sol-gel materials.